1. Field of the Invention
The present invention relates to an automatic perimeter for automatically examining the field of vision of a patient's eye. More specifically, the present invention pertains to an automatic perimeter which is designed to automatically present marks or stimuli in accordance with various conditions including brightness, positions, presentation time and presentation intervals of the marks.
2. Description of the Prior Art
In general, a perimeter has a hemispherical concave screen on which stimuli are presented. In such perimeter, a patient's eye to be examined is located at the center of the sphere of the screen and the sight axis of the eye is fixed to the center of the screen by having the eye see a fixed viewing target on the screen. Then, the stimuli are presented in accordance with various conditions in sequence at various positions on the screen with different sizes and different brightness so as to distinguish visible zone from invisible zone.
In conventional automatic perimeters, presentations of the stimuli are automatically made upon initiation of the operation in accordance with a predetermined schedule until presentations of all stimuli are completed so as to reduce a burden to the operator. It should however be noted that it may sometimes be required to stop the presentation of the stimuli. For example, when the operator finds that the sight axis is not fixed to the center of the screen, the operation must be interrupted to repeat past steps of the operation. Further, when the operator believes that he could obtain data sufficient to determine the visual field, further measuring steps may no longer be necessary. In order to make it possible to perform such control, the conventional perimeter includes manual switches or photoelectrical switches. It should however be noted that such switches are inconvenient to actuate because the examination must be carried out in a dark room, and the operator must continue to ensure that the sight axis is fixed to the center of the screen during the examination so that it is difficult to locate an appropriate switch.
Further, when it is found during an examination that the sight axis is offset from the center of the screen, there is a high possibility of errors being produced due to such offset of the sight axis in a certain number of perception data already obtained. Therefore, if presentations of the stimuli are restarted to examine the eyesight with all of the data already obtained being used for determining the viewing field, it is difficult to maintain the accuracy of the examination.